The popularity of combat sports and especially Mixed Martial Arts (MMA), through the Ultimate Fighting Championship (UFC) fights, has been growing fast, with a large number of athletes being involved in MMA training and fights (La Bounty et al., 2011), while the number of spectators and fans has also increased rapidly (Andrew et al. 2009). MMA may be characterized as an intermittent sport with high speed and power activity bursts (James et al., 2016; Lenetsky and Harris, 2012), recurring for three to five 5-minute rounds with 1 minute rest between each round (La Bounty et al., 2011). Thus, MMA is a highly physiologically complex sport, in which a wide spectrum of physical abilities (i.e., strength, power, speed, muscular endurance) and metabolic mechanisms (anaerobic and aerobic) are involved during training and competition (James et al., 2016; Lenetsky and Harris, 2012). MMA athletes are required to use and combine different fight techniques (James et al., 2017a), as well as to have high levels of strength, power, speed, anaerobic power and aerobic fitness, in order to endure the 3-5 rounds of high intensity intermittent efforts (James et al., 2016; Lenetsky and Harris, 2012). These high physical and technical demands stress the necessity for specialized strength and conditioning training programs for these athletes (James et al., 2013; 2016; Lenetsky and Harris, 2012).

There is a limited number of studies and reports that investigated or described the training practices and guidelines for MMA athletes (Amtmann, 2004; Amtmann and Berry, 2003; La Bounty et al., 2011; Lenetsky and Harris, 2012; Tack, 2013). Although the physiological characteristics of successful MMA athletes and the physiological demands of the sport have been recently described and examined (Amtmann et al., 2008; James et al.; 2016; 2017a; 2017b; La Bounty et al., 2011; Lenetsky and Harris; 2012), there is still a need to determine effective training programs. Previous reports suggested that there may be a large variability in strength and conditioning training programs among MMA athletes, while the large volume and high demands of training and competing may lead to fatigue, overreaching or overtraining (James et al., 2013; La Bounty et al., 2011).

High intensity interval training (HIIT) has been proposed as an effective training method to achieve metabolic conditioning and improve aerobic fitness in MMA (James et al., 2013; La Bounty et al., 2011; Tack, 2013). Also, strength, power and complex training as well sport-specific movements using light loads, have also been suggested to improve power and speed of MMA athletes (Tack, 2013). Thus, the purpose of the present study was to compare the effectiveness of a 4-week regular strength and conditioning training program based on circuit training and characterized by high-volume, with a low-volume conditioning training program, including strength and power training, HIIT, and sport specific power exercises, i.e. exercises that are biomechanically similar to movements performed during MMA, such as medicine ball throws simulating a punch. It was hypothesized that the latter program, despite its lower volume and perceived effort, would confer greater improvements in performance parameters that are important for MMA.

Methods

General design

A two group training study was used to compare the effects of a short-term complementary sport-specific strength and conditioning program with a "regular" strength and conditioning training program commonly used by most MMA fighters. Seventeen experienced fighters were divided according to their pre-training maximum back-squat strength (1RM), into two groups: (A) Specific Training Group (STG, n = 10), which followed a specific strength and conditioning program designed according to the demands of MMA competition and (B) Regular Training Group (RTG; n = 7), in which participants followed a regular strength and conditioning program that is commonly used by MMA athletes. The training intervention lasted 4 weeks, with athletes performing STG or RTG three times per week every 48 hours (Monday, Wednesday, Friday) according to their group assignment, while on the intermediate three days (Tuesday, Thursday, Saturday), all athletes followed the same fighting training focused on technical skills, striking and grappling. During the first visit to the laboratory, athletes were examined by a trained physician for limiting health impediments and they were asked to complete a weekly recall of self-reported physical activity and a medical history questionnaire. Anthropometric assessment and body composition evaluation was also performed. In the second and third visits, they were familiarized with the testing procedures by performing all tests twice. One week after the last familiarization session, the following physical fitness parameters were evaluated with 48 h intervals between tests: (A) Sprint performance, (B) muscle strength, (C) power and (D) aerobic fitness. One week after the end of the intervention these evaluations were repeated. All tests were performed during the morning hours. At least two of the co-authors were present during testing and verbally encouraged the athletes. The best performance in each test was recorded and used in the statistical analysis. During the experimental period, all participants abstained from any other form of physical training, competition, or other strenuous physical activity. In addition, they were instructed to retain their regular eating habits during the training period. To avoid any effects of the last training sessions on performance evaluation, all post-training assessments were performed at least one week from the last training session.

Participants

Responders to a written announcement of the study posted at the local MMA gyms and clubs, reported to the laboratory and were informed about the study protocols and the inclusion criteria. They were asked to complete a weekly recall self-reported questionnaire to determine their level of physical activity, training experience, frequency, duration per session, and total weekly workload. After evaluation of the responders' applications, seventeen professional, national level male MMA athletes who fulfilled the inclusion criteria (described below), underwent the pre-training fitness evaluation and were then assigned according to their squat 1RM (Table 2), into two groups: (A) Specific Training Group (STG; n = 10; age: 28.9 [+ or -] 4.2 years, height: 1.81 [+ or -] 0.04 m; number of professional bouts: 4.2 [+ or -] 2.5; wins: 2.6 [+ or -] 1.7; losses: 1.6 [+ or -] 1.0) and (B) Regular Training Group (RTG; n = 7; age: 25.7 [+ or -] 5.0 years, height: 1.75 [+ or -] 0.05 m; number of professional bouts: 3.8 [+ or -] 2.0; Wins: 2.4 [+ or -] 1.5; losses: 1.4 [+ or -] 0.9). Initially, 10 athletes were enrolled in the RTG group, however, three of them did not complete the training program due to personal reasons unrelated to the study. The inclusion criteria were: 1) at least three years of systematic MMA training, 2) at least one recent professional fight (

Training

Athletes completed a 4-week training program. Strength and conditioning training was performed three times per week every 48 hours (Monday, Wednesday, Friday), according to the group assignment. On the intermediate three days (Tuesday, Thursday, Saturday), all athletes followed the same fighting training, focused on technical skills, striking and grappling. All participants rested for one day per week (Sunday). The characteristics of the training programs for the STG and RTG are presented in Table 1.

Strength and conditioning sessions, started with a 10-min low intensity warm-up, followed by dynamic stretching exercises of the major muscle groups. STG performed a periodized compound strength and conditioning training program with the first and the third session per week composed mainly of strength and power exercises. Strength exercises included the squat, bench press and deadlift at 80-95% of 1RM. The number of sets, repetitions and the loads used are shown in Table 1. Each squat, bench press and deadlift set was followed by three counter-movement jumps with maximum intensity, medicine ball chest throws (2 kg) and loaded Jump Shrugs with the 45% of deadlift 1RM respectively, with 1 min rest between the 3 reps of each power exercise. Accordingly, 10 min after the end of the strength exercises, athletes of the STG performed a High Intensity Interval Aerobic Training (HIIT) on a rowing ergometer, according to a recently reported protocol (Stevens et al., 2015). The rowing ergometer was preferred over a treadmill, according to evidence presented in a review on combat sport athletes, suggesting more advantageous adaptations in aerobic and anaerobic capacity after rowing training compared with cycling or treadmill exercise, at least in fighters (Kendall and Fukuda, 2011). The STG in the first week completed 5 sets of 60 s all out ergometer sprints (115% of power achieved at the fastest 500 m part of the 2000 m rowing ergometer evaluation of aerobic fitness, as described below) with 4 min passive recovery between each set (Stevens et al., 2015). In the second week, the STG completed 6 sets of 60 s all out sprints on rowing ergometer and on the 3rd & 4th week the sets remained unchanged but the passive recovery was reduced to 3.5 and 3 min for weeks 3 and 4 (Table 1).

The second session in each week was composed of exercises aiming to increase athletes' power and speed. All athletes of STG started their sessions with loaded jump squats in a smith machine (Table 1). Participants, rested for 4 min between sets, during which they performed 8 drop jumps from a 40.7 [+ or -] 16.7 cm box (range 15 - 60 cm), according to athletes' optimal drop height, defined as that at which they achieved the highest reactive strength index (RSI; Byrne et al., 2010; Details about the determination of the optimal drop height are...